Prime Minister Arseniy Yatsenyuk is urging Ukrainians to vote in the country's May 25 presidential election to "defend Ukraine."

Yatsenyuk, in a statement on May 24, told Ukrainians they have a responsibility to vote despite threats by "bandits sponsored from abroad" to disrupt the election.

Pro-Russian separatists have vowed to block voting in areas they control in the east of the country.

The days before the election have also seen a resurgence in fighting between government forces and the separatists who have declared their own so-called "people's republics" in the east.

Russian President Vladimir Putin has said Moscow would "respect" the outcome of the election. But he also said Ukraine has descended into what he described as "chaos and full-scale civil war."

Speaking on May 24, Putin reiterated that Moscow would work with Ukraine's new president. But he also said that the winner of the May 25 presidential election may turn out to be a "transitional figure."

Ukrainian Prime Minister Arseniy Yatsenyuk

In his statement on May 24, Yatsenyuk said he was sure the winner of the election will make a priority of signing a key political and free trade agreement with the European Union.

Moscow-backed President Viktor Yanukovych's decision not to sign such a deal triggered months of mass protests that ended when he fled to Russia in February.

The election pits front-runner Petro Poroshenko, a 48-year-old confectionary magnate, against some 20 other challengers -- including former Prime Minister Yulia Tymoshenko.

Political analysts are predicting a second round vote between Poroshenko and Tymoshenko on June 15.

Yatsenyuk said the vote will be an expression "of the will of Ukrainians from the west, east, north and south."

In eastern Donetsk and Luhansk regions, however, pro-Russian rebels have seized or blocked the offices of around half of the election commissions, in some cases kidnapping and intimidating election officials.

Denis Pushilin, one of the leaders of the so-called "Donetsk People's Republic" threatened that "if necessary," on May 24 the insurgents will use force to prevent voting taking place.

Authorities say they have mobilized tens of thousands of police and volunteers to try to ensure security on polling day.